The embryotoxic, cytogenetic and carcinogenic effects of new as well as clinically useful antitumor agents are under investigation. Studies on the embryotoxic effects in mice of anthracenedione, dihydroxyanthracenedione and spirogermanium have been completed. The carcinogenic activity of various clinically effective antitumor and/or immunosuppressive agents, including procarbazine, N-methylnitrosourea, melphalan, azathioprine, adriamycin, and cyclophosphamide, is under evaluation in long-term studies in monkeys. A survey of second malignancies developing in treated cancer patients, initiated several years ago, is continuously being updated using data from published reports and from several centers and hospitals. The possibility of preventing drug-induced infertility in males by suppressing spermatogenesis prior to, and during, administration of cyclophosphamide or procarbazine is being evaluated in mice.